Liquid pharmaceutical compositions comprising a drug bound to an ion exchange resin have been known for many years. For instance, British patent 869,149 discloses the adsorption of ionizable drugs on ion-exchange resins and the dispersion of the resultant solids in a carrier liquid, and German patent 2,246,037 discloses drug adsorbed on resin particles, which loaded resin particles are then coated with a water-insoluble film-forming resin such as a polyacrylic acid ester. Solid compositions comprising ion-exchange resins are disclosed, for example, in EP 249,949 to Sellassie et al.
More recent publications disclose further treatment of drug-ion-exchange resin particles in order to improve sustained release characteristics. For example, U.S. Pat. No. 4,221,778 to Raghunathan discloses ion exchange resin-drug complexes treated with an impregnating agent such as polyethylene glycol or propylene glycol prior to coating with a water-permeable diffusion barrier such as ethylcellulose; the impregnating treatment is said to prevent swelling and, fracturing of the resin particle in solutions and to improve coatability. EP 171,528 to the same inventor discloses a similar resin treatment using glycerine to improve coatability. EP 254,811 and EP 254,822 both to Raghunathan and Chow, disclose similar impregnation of sulfonic cation exchange resins with agents such as hydroxypropylmethylcellulose and with high molecular weight polymers, respectively, to improve coatability. EP 139,881 to Shuemaker discloses compositions in which all ionic components having the same charge are present as resin complexes, thereby overcoming variations in the dissolution profile caused by ionic substances in the formulation.